Now and again there is concern over the possibility of people creating more than one user account and pretending to be two seperate people.

Because of this I have often been asked to check whether or not the IP address of one user is the same as the IP address of another user.

There are two seperate issues here that I would like to clarify and explain about...

1. Creating multiple user accountsThis, in itself, it not against the rules. I think there are valid reasons why one regular poster might want to post anonymously once in a while. Having said that, it would not be good if someone created multiple accounts in order to cause mischief - that obviously is against the rules.

2. IP AddressesOn its own an IP address can not show that one user is the same person as another user.

One ISP only has a limited number of IP addresses, so they get shared around and are randomly allocated when someone logs on to the Internet, so it is perfectly possible for one person to have had the same IP as many other people at different times. This is true whether you have broadband or dial-up, cable or BT. Very few people with an ordinary Internet connection have a 'static IP address' - which means one that doesn't change - and even if they do, they can hide it with a fake one.

Large organisations such as schools and colleges often have one or more static IP addresses that don't change. However, because of the large number of people using their computers it is not possible for us to say that one user was the same person as another user - only that they may have used the same computer.

So really the IP address doesn't proove very much at all - even though people seem to think it does. Still, don't get too comfortable because the ISP can tell who was online at what time with which IP address! And that's why NOTHING is truly private on the Internet!

Just to illustrate how impossible it is for me to tell whether or not one user is the same person as another user see below for a list of people who have posted on this site from just one particular IP adress - I'm sure they're not all the same person!